Neural correlates exist for a basic component of logical formulae, PREDICATE(x). Vision and audition research in primates and humans shows two independent neural pathways; one locates objects in body-centered space, the other attributes properties, such as colour, to objects. In vision these are the dorsal and ventral pathways. In audition, similarly separable “where” and “what” pathways exist. PREDICATE(x) is a schematic representation of the brain's integration of the two processes of delivery by the senses of the location of an arbitrary referent object, mapped in parietal cortex, and analysis of the properties of the referent by perceptual subsystems.

The brain computes actions using a few “deictic” variables pointing to objects. Parallels exist between such nonlinguistic variables and linguistic deictic devices. Indexicality and reference have linguistic and nonlinguistic (e.g., visual) versions, sharing the concept of attention. The individual variables of logical formulae are interpreted as corresponding to these mental variables. In computing action, the deictic variables are linked with “semantic” information about the objects, corresponding to logical predicates.

Mental scene descriptions are necessary for practical tasks of primates, and preexist language phylogenetically. The type of scene descriptions used by nonhuman primates would be reused for more complex cognitive, ultimately linguistic, purposes. The provision by the brain's sensory/perceptual systems of about four variables for temporary assignment to objects, and the separate processes of perceptual categorization of the objects so identified, constitute a pre-adaptive platform on which an early system for the linguistic description of scenes developed.

Formal logic may be an inappropriate framework for understanding perception. The responses of neurons at various levels of the sensory hierarchy may be better described in terms of probability than logic. Analysis and modeling of the multisensory responses of neurons in the midbrain provide a case study.

The representations formed by the ventral and dorsal streams of a prelinguistic agent will tend to be too qualitatively similar to support the distinct roles required by PREDICATE(x) structure. We suggest that the attachment of qualities to objects is not a product of the combination of these separate processing streams, but is instead a part of the processing required in each. In addition, we suggest that the formation of objective predicates is inextricably bound up with the emergence of language itself, and so cannot be cleanly identified with any prelinguistic cognitive capacities.

Hurford argues that propositions of the form PREDICATE(x) represent conceptual structures that predate language and that can be explicated in terms of neural structure. I disagree, arguing that such predicates are descriptions of limited aspects of brain function, not available as representations in the brain to be exploited in the frog or monkey brain and turned into language in the human.

While the PREDICATE(x) structure requires close coordination of subject and predicate, both represented in consciousness, the cognitive (ventral), and sensorimotor (dorsal) pathways operate in parallel. Sensorimotor information is unconscious and can contradict cognitive spatial information. A more likely origin of linguistic grammar lies in the mammalian action planning process. Neurological machinery evolved for planning of action sequences becomes applied to planning communicatory sequences.

Hurford's argument suffers from two major weaknesses. First, his account of neural mechanisms suggests no place in the brain where the two halves of a predicate-argument structure could come together. Second, his assumption that language and cognition must be based on logic is neither necessary nor particularly plausible, and leads him to some unlikely conclusions.

The objects of attention can be located anywhere along the causal link from the source of stimuli to the final output of the vision system. As causes, they attract and control attention, and as products, they constitute targets of analysis and explicit comments. Stimulus-driven indexing creates pointers that support fast and frugal cognition.

Hurford claims that empty variables antedated proper names in linguistic (not merely logical) predicate-argument structure, and this had an effect on visual perception. But his evidence, drawn from proper names and the supposed inability of nonhumans to recognise individual conspecifics, is weak. So visual perception seems less relevant to the evolution of grammar than Hurford thinks.

Hurford's discussion also vindicates the classical empiricist program in semantics. The idea that PREDICATE(x) is the logical form of the sensory representations encoded via the dorsal and ventral streams validates empiricists' insistence on the psychological primacy of sense data, which have the same form. In addition to knowing the logical form of our primitive representations, however, we need accounts of (1) their contents and (2) how more complex thoughts are derived from them. Ideally, our semantic vocabulary would both reflect the psychological “primitiveness” of these representations and make clear how more complex representations derive from them.

Predicates involved in language and reasoning are claimed to radically differ from categories applied to objects. Human predicates are the cognitive result of a contrast between perceived objects. Object recognition alone cannot generate such operations as modification and explicit negation. The mechanism studied by Hurford constitutes at best an evolutionary prerequisite of human predication ability.

In the context of Hurford's claim that “some feature of language structure maps onto a feature of primitive mental representations,” I will argue that Hurford's focus on 1-place predicates as the basis of the “mental representations of situations in the world” is problematic, particularly with respect to spatiotemporal events. A solution is proposed.

Considerations from an interaction-based approach to the evolution of language and the role of word-sentences therein show that the object-attribute ontology is arrived at a much later stage. Therefore, Hurford's arguments, by focusing on the predicate-argument structure, seem to miss out on most of the interesting aspects of the early stages in language evolution.

Philosophical accounts of thought crucially involve an array of abilities to identify general properties or features of the world (corresponding to concepts) and objects that instantiate those general properties. Abilities of both types can be grounded in a naturalistic account of the usefulness of cognitive structures in adaptive behaviour. Language enhances these abilities by multiplying the experience bases giving rise to them and helping to overcome subjective biases.

The predicate-argument approach, focused on perception, is compared with the ease-of-predication (or predicability) approach, focused on encyclopedic knowledge. The latter offers functional prediction and implementation in connectionist models. However, the two approaches characterise predicates in different ways. They thus resemble predicational cantilevers built out from opposite sides of cognition, with a gap that is yet to be bridged.

Predicate logic has proved a very useful tool for the expression of theories of natural language semantics. Hurford's suggestion that predicate–argument structures mirror certain properties of the human sensorimotor architecture can be seen as an explanation of why this is so. Although I support this view, I think that the correspondences that Hurford draws between linguistic and sensorimotor structures not only involve natural language semantics, but include some elements of natural language syntax as well.

According to Hurford, PREDICATE (x) is correlated with deictic object variables during event perception. This claim is inconsistent with some core literature on the perception of motion events. We point out that the perception of events involves the activation of the modal properties and amodal properties of underlying event structure, for which Hurford's target article fails to account.

Hurford presents a much-needed lowly origins scenario for the evolution of conceptual precursors to lexical items. But more is still needed on action, regarding both the message level of lexical concepts and the medium. We summarize our complementary action-based lowly origins (frame/content) scenario for the vocal auditory medium of language, which, like Hurford's scenario, is anchored in a phylogenetically old neurological dichotomy.

While the search for the neural basis of the language of thought is a laudable enterprise, and the article by Hurford a valiant first attempt, we argue that in investigating the argument structure of natural language it will ultimately prove more fruitful to consider the restrictions forced on the system by its inherently syntactic character.

It is argued that, in the traditional subject-predicate sentence, two interpretations of the subject term coexist, one intensional and the other extensional, which explains the superficial difference between the traditional S-P relation and the predication of predicate logic. Data from psychological studies of syllogistic reasoning support the view that the contrast between predicate and argument is carried over to the traditional S-P sentence.

Experimental data suggest that the division between the visual ventral and dorsal pathways may indeed indicate that static and dynamical information is processed separately. Contrary to Hurford, it is suggested that the ventral pathway primarily generates representations of objects, whereas the dorsal pathway produces representations of events. The semantic object/event distinction may relate to the morpho-syntactic noun/verb distinction.